Development of a ruthenium multi-pyridine complex as photosensitizer for highly efficient light driven water oxidation

As we all know, the photosensitizer is the vital role in photocatalytic water oxidation system. In this paper, a novel [Ru(bpy)₂(tpphz)](PF₆)₂ complex (PS1) was synthesized and characterized fully. And, it displayed a higher photoactivity (TON, 110) than [Ru(bpy)₃](PF₆)₂ (PS2) (TON, 62) and [Ru(bpy)₂(dcb)](PF₆)₂ (PS3) (TON, 82) for water oxidation in a three-component system with Ru(bda)(isoq)₂ as catalyst. The main reason for the enhancement of photocatalytic activity should be that the π-π stacking supramolecular interaction between the π-tpphz ligand of the PS1 and the π-isoq ligand of the catalyst increased the intermolecular interaction between PS1 and catalyst, and promoted the molecular aggregation and accelerated valid electronic transmission. Nevertheless, a modest driving force of PS1 for photocatalysis water oxidation should be another contribution.     

HPLC separation,NMR and QTOF/MS/MS structure elucidation of a prominent nitric oxide donor agent based on an isomeric composition of a nitrosyl ruthenium complex

A new and promising nitrosyl ruthenium complex, [Ru(NO)(bdqi-COOH)(terpy)](PF₆)₃, bdqi-COOH is 3,4-diiminebenzoic acid and terpy is 2,2′-terpyridine, has been synthesized as a NO donor agent. The procedure used for [Ru(NO)(bdqi-COOH)(terpy)](PF₆)₃ synthesis has, apparently, yielded the formation of two isomers in which the ligand bdqi-COOH appears to be coordinated in its reduced form (bdcat-COOH), which could have differences in their pharmacological properties. Therefore, it was intended to separate the two possible isomers by high-performance liquid chromatography (HPLC) and to characterize them by high resolution mass spectrometry (QTOF MS) and by magnetic nuclear resonance spectroscopy (NMR). The results obtained by MS showed that the ESI-MS mass spectra of both HPLC column fractions, e.g. peak 1 and peak 2, are essentially equal, showing that both isomers display nearly identical gas-phase behavior with clusters of isotopologue ions centered at m/z 573, m/z 543 and m/z 513. Regarding the NMR analysis, the results showed that the positional isomerism is located in the bdqi-COOH ligand. From the observed results it can be concluded that the synthesis procedure that has been used results in the formation of two [Ru(terpy)(bdqi-COOH)NO](PF₆)₃ isomers.     

Bis(dipyridophenazine)(2‐(2′‐pyridyl)pyrimidine‐4‐carboxylic acid)ruthenium(II) Hexafluorophosphate: A Lesson in Stubbornness

Ruthenium complexes are currently considered to be among the most promising alternatives to platinum anticancer drugs. In this work, thirteen structural analogues and organelle/receptor‐targeting peptide bioconjugates of a cytotoxic bis(dppz)‐Ru^II complex [Ru(dppz)₂(CppH)](PF₆)₂ ( 1 ) were prepared, characterized, and assessed for their cytotoxicity and cellular localization (CppH=2‐(2′‐pyridyl)pyrimidine‐4‐carboxylic acid; dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine). It was observed that structural modifications (lipophilicity, charge, and size‐based) result in the cytotoxic potency of 1 being compromised. Confocal microscopy studies revealed that unlike 1 , the screened complexes/bioconjugates do not have a preferential accumulation in mitochondria. The results of this important structure–activity relationship strongly support our initial hypothesis that accumulation in mitochondria is crucial for 1 to exert its cytotoxic action.     

Redox-induced linkage isomerization detected in [Ru(NH3)5(NVF)](PF6)2(NVF = N-vinylformamide)

A new ruthenium (II) complex, of formula [Ru(NH₃)₅(NVF)](PF₆)₂, 1 (with NVF = N-vinylformamide) was synthesized and characterized by chemical analyses, spectroscopic and electrochemical techniques. The presence of two coordination sites within NVF makes complex 1 capable of showing a redox-dependent linkage isomerization process, which was detected by cyclic voltammetry and spectroelectrochemical measurements. Upon oxidation of the metallic center from Ru (II) to Ru (III) of complex 1 in N,N-dimethylformamide, linkage isomerization takes place from a vinyl-coordinated Ru(II) to an amide-coordinated Ru(III). This is an additional example of a system that can be applied in molecular memory devices or engines of a molecular machine.     

Mild oxidation of alcohols with periodic acid catalyzed by [Ru(acac)2(CH3CN)2]PF6 in water

A facile [Ru(acac)₂(CH₃CN)₂]PF₆ (Hacac = acetylacetone) (1) catalyzed oxidation of alcohols to aldehydes or ketones using H₅IO₆ as oxidant in water at room temperature is described.     

A donor–chromophore complex containing the polyazine bridging ligand 2,3-bis(2-pyridyl)pyrazine

The complex [(PTZpbpy)₂Ru(dpp)](PF₆)₂ coupling a phenothiazine derived electron donor to a ruthenium complex with a polyazine bridging ligand dpp (PTZpbpy = 4-methyl-4′-(4-(N-phenothiazinato)pentyl)-2,2′-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine) has been synthesized and the redox, spectroscopic, and excited state properties elucidated. In the coupled electron donor system, the emission intensity from the Ru(dπ) → dpp(π¹) ³MLCT state is quenched by 94% of that of the analogous system [(bpy)₂Ru(dpp)](PF₆)₂ (bpy = 2,2′-bipyridine) which lacks a coupled electron donor. Coupling a donor–chromophore unit to a bridging ligand will allow the expansion of the molecular architecture to form complex molecular assemblies which contain covalently attached electron donors.     

The Reaction of Tertiary Anilines with Maleimides under Visible Light Redox Catalysis

Tertiary anilines can be prompted to react with N‐aryl‐ and N‐benzylmaleimides to form tetrahydroquinoline products under photocatalysis using visible light irradiation, the ruthenium or iridium complexes Ru(bpy)₃Cl₂ or Ir(ppy)₂(dtbbpy)PF₆ as catalyst, and air as terminal oxidant.     

Ruthenium‐Catalyzed O‐Allylation of Phenols from Allylic Chlorides via Cationic [Cp*(η3‐allyl)(MeCN)RuX][PF6] Complexes

The [Cp*(MeCN)₃Ru(II)][PF₆] complex is an efficient catalyst precursor for the O‐allylation of phenols with allylic chlorides in the presence of K₂CO₃ under mild conditions. This ruthenium precursor affords branched allyl aryl ethers according to a regioselective reaction, which contrasts with the uncatalyzed nucleophilic substitution from the same substrates. Stable (η³‐allyl)Ru(IV) cationic complexes resulting from the reaction of [Cp*(MeCN)₃Ru][PF₆] with allylic halides were identified as intermediate catalytic species. An X‐ray structure determination of the complex [Cp*(MeCHCHCH₂)(MeCN)RuBr][PF₆] disclosed an (endo‐trans‐MeCHCHCH₂) allylic ligand. The structural information obtained from the study of Cp*(allyl)Ru(IV) complexes indicated that electronic effects at the coordinated allylic ligand likely account for the better regioselectivity obtained from cinnamyl chloride as compared to aliphatic allylic chlorides.     

Strong metal-to-ligand π-backbonding weakens the NN bond in 2-pyridinealdazine coordinated to tetraammine-ruthenium(II)

A new mononuclear Ru(II) complex of formula [Ru(NH₃)₄(2-PCA)](PF₆)₂, (1), with 2-PCA = 2-pyridinealdazine, has been synthesized and characterized by spectroscopic and electrochemical techniques. The complete structure of (1) was determined by X-ray diffraction. A strong π-backbonding effect d_π(Ru) → π *(2-PCA) is disclosed in (1) by the high value of the Ru^III/Ru^II redox potential and the short Ru-N(imine) bond length, which leads to a weakened NN bond in coordinated 2-PCA compared to that of the free ligand and thus to an enhanced reactivity in acidic media. In effect, the product of the reaction of excess Ru with 2-PCA is not the dinuclear species bridged by 2-PCA, but the already known 2-iminopyridine complex of tetraammineruthenium(II). DFT and TD-DFT calculations of (1) were consistent with experimental results and allowed the complete assignment of its UV–Visible bands.     

A new family of trinuclear Ru(II) polypyridyl complexes acting as pH-induced fluorescence switch

Tripodal ligands 1,3,5-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)methyl}-2,4,6-trimethylbenzene (L¹), 1,1,1-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)methyl}propane (L²), 2,2′,2′′-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)ethyl}amine (L³), and corresponding Ru(II) complexes [(bpy)₆L^1–3(Ru^II)₃](PF₆)₆, shortly called (Ru–L^1–3), have been synthesized. UV–vis absorption and fluorescence spectra of these complexes are both strongly dependent on the pH of the buffer solution. These complexes act as pH-induced off–on–off fluorescence switch through protonation and deprotonation of the imidazole-containing ligands.     

Organometallic Derivatives of Cyclotriphosphazene as Precursors of Nanostructured Metallic Materials: A New Solid State Method

The cyclic phosphazene trimers [N₃P₃(OC₆H₅)₅OC₅H₄N·Ti(Cp)₂Cl][PF₆] (3), [N₃P₃(OC₆H₄CH₂CN·Ti(Cp)₂Cl)₆][PF₆]₆ (4), [N₃P₃(OC₆H₄-Bu^t)₅(OC₆H₄CH₂CN·Ti(Cp)₂Cl)][PF₆] (5), [N₃P₃(OC₆H₅)₅C₆H₄CH₂CN·Ru(Cp)(PPh₃)₂][PF₆] (6), [N₃P₃(OC₆H₅)₅C₆H₄CH₂CN·Fe(Cp)(dppe)][PF₆] (7) and N₃P₃(OC₆H₅)₅OC₅H₄N·W(CO)₅ (8) were prepared and characterized. As a model, the simple compounds [HOC₅H₅N·Ti(Cp)₂Cl]PF₆ (1) and [HOC₆H₄CH₂CN·Ti(Cp)₂Cl]PF₆ (2) were also prepared and characterized. Pyrolysis of the organometallic cyclic trimers in air yields metallic nanostructured materials, which according to transmission and scanning electron microscopy (TEM/SEM), energy-dispersive X-ray microanalysis (EDX), and IR data, can be formulated as either a metal oxide, metal pyrophosphate or a mixture in some cases, depending on the nature and quantity of the metal, characteristics of the organic spacer and the auxiliary substituent attached to the phosphorus cycle. Atomic force microscopy (AFM) data indicate the formation of small island and striate nanostructures. A plausible formation mechanism which involves the formation of a cyclomatrix is proposed, and the pyrolysis of the organometallic cyclic phosphazene polymer as a new and general method for obtaining metallic nanostructured materials is discussed.     

Switching on the photochemical reactivity in heterodimetallic Os–Ru bipyridyl complexes containing a bis(bidentate) phosphine

For the first time the excited states of the RuP₂N₄ moiety belonging to a new heterodimetallic Os^II–Ru^II bipyridyl complex are successfully designed in order to introduce photochemical reactivity. This dramatic effect is achieved via the use of the sterically demanding bis(bidentate) phosphine cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb). Thus, the temperature dependence of the luminescence lifetimes ranging from 77 to 298 K for the novel homodimetallic species meso-(ΔΛ/ΛΔ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (1) and rac-(ΔΔ/ΛΛ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (2) clearly indicates that the d–d state responsible for photochemistry is not populated. By contrast, the analogous temperature dependence for the new heterodimetallic species ΔΛ/ΛΔ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (3) and ΔΔ/ΛΛ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (4) unequivocally shows that as a consequence of the population of the d–d state the photochemical reactivity is switched on. Since single crystal X-ray structure analyses are a major clue to the understanding of photophysical and photochemical properties, also the X-ray structures of 1–3 are given.     

Photolysis of [Ru(bipy)2(NO)Cl](PF6)2 in frozen ionic glass matrices. Evidence for nitrosyl linkage isomerism and NO-loss in a physiologically relevant nitric oxide source

Photolysis of [Ru(bipy)₂(NO)Cl](PF₆)₂ and its ¹⁵NO isotopomer in frozen butyl, methylimidazole (bmim) PF₆ glass at ca. 90 K results in appearance of bands characteristic of isonitrosyl and side-on nitrosyl linkage isomers. In addition, weak bands corresponding to free NO in the matrix are also observed. These observations suggest that weakly bound linkage isomers of nitric oxide are likely intermediates in the photolytic release of NO in this and other physiologically relevant NO sources.     

The effect of pH on the emission and absorption spectra of a ruthenium complex

A ruthenium complex, Ru(Phen)₂(Phen-OH-CO₂Et)²⁺(PF₆)₂, where Phen=1,10-phenanthroline and Phen-OH-CO₂Et=3-carbethoxy,4-hydroxy-1,10-phenanthroline ligands has been synthesized. The emission intensity of this complex changes in the pH range of 3–11, which makes it useful in the design of chemosensors.     

Heteroleptic chromium(III) tris(diimine) [Cr(N^N)2(N′^N′)]3 + complexes

A series of heteroleptic tris(diimine) complexes of chromium(III) is reported and the crystal structures of {4[Cr(bpy)₂(phen)][PF₆]₃}·11MeCN and 4[Cr(4,4′-Me₂bpy)₂(bpy)][PF₆]₃}·12MeCN·H₂O are described. The combined effects of a 1:3 cation: anion ratio and lattice solvent molecules are discussed, in particular in the context of the influence on intercation embraces. The presence of the methyl substituents in {4[Cr(4,4′-Me₂bpy)₂(bpy)][PF₆]₃}·12MeCN·H₂O results in Me–π_bpy contacts becoming the dominant packing interactions and in the assembly of motifs distinct from those in {4[Cr(bpy)₂(phen)][PF₆]₃}·11MeCN.     

Aldehyde-decorated 2,2′-bipyridine and 2,2′:6′,2″-terpyridine ruthenium(II) complexes: Convenient scaffolds for supramolecular chemistry

Two new aldehyde-decorated tpy and bpy-containing ruthenium(II) complexes, [Ru(1)(bpy)₂][PF₆]₂ and [Ru(1)(tpy)Cl][PF₆] in which 1 is 5,5′-bis(4-formylphenyl)-2,2′-bipyridine, have been prepared and fully characterized. The packing in both solid state structures involves extensive O_aldehyde···HC_pyridine contacts, but π-stacking interactions are important only between [Ru(1)(tpy)Cl]⁺ cations.     

WGSR catalyzed by cis-[Rh(CO)2(amine)2]PF6 heterogenised on poly(4-vinylpyridine)

This paper describes catalytic activation studies of the water–gas shift reaction by cis-[Rh(CO)₂(amine)₂]PF₆ (amine = 4-picoline, 3-picoline, 2-picoline, pyridine, or 2,6-lutidine) heterogenised on poly(4-vinylpyridine) in aqueous 2-ethoxyethanol. The effect of varying the nature of the amine was investigated. The rhodium complexes bearing 4-picoline (4-pic) ligands proved to be most active among those surveyed, and displaying turnover frequencies for hydrogen production of 8.9 mol of H₂ per mole of Rh per day for 9.4x10^-5 mol cis-[Rh(CO)₂(4-pic)₂]PF₆/1.00 g poly(4-vinylpyridine), P(CO) = 0.9 atm at 100°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nickel(II) thiolates derived from transmetallation reaction of [Zn(Tab)4](PF6)2 with Ni(II) ions and their catalytic activity toward the CN coupling reactions

Reactions of NiCl₂·6H₂O or Ni(ClO₄)₂·6H₂O with 2,2′-bipyridine (2,2′-bipy), or 2-bis(diphenylphosphino)ethane (dppe) or 1,4-bis(diphenylphosphino)butane (dppb) followed by addition of [Zn(Tab)₄](PF₆)₂ (1) resulted in the formation of one trinuclear cationic complex [(2,2′-bipy)₄Ni₃(μ-Tab)₄]Cl_0.5(PF₆)_5.5 (2), one mononuclear cationic complex [Ni(Tab)₂(dppe)](PF₆)₂ (3), and one dinuclear cationic complex [Ni₂(dppb)(μ-Tab)₂(Tab)₂](PF₆)₂(ClO₄)₂ (4). Complexes 2–4 were characterized by elemental analysis, IR, UV–vis, ¹H and ³¹P NMR, and single-crystal X-ray diffraction. In the [(2,2′-bipy)₄Ni₃(μ-Tab)₄]^6 + hexacation of 2, the central Ni(II) atom is connected to two [Ni(2,2′-bipy)₂]^2 + fragments by two pairs of μ-Tab ligands, forming a linear trinuclear cationic structure. The Ni(II) center of the dication of 3 is tetrahedrally coordinated by two S atoms from two Tab ligands and two P atoms of one dppe ligand. Complex 4 has a dimeric cationic structure in which two [(Tab)Ni]^2 + species are linked by a pair of μ-Tab ligands and one dppb ligand. Complexes 2–4 displayed high catalytic activity toward the cross-coupling reactions of arylboronic acids and amines to produce N-arylated amines.     

Use of HPLC in the identification of cis and trans-diaquabis(2,2′-bipyridine)ruthenium(II) complexes: crystal structure of cis-[Ru(H2O)2(bpy)2](PF6)2

[Ru(H₂O)₂(bpy)₂](PF₆)₂ complex was obtained by reacting HPF₆ in a [Ru(CO₃)(bpy)₂] aqueous solution. The complex can exist as cis and trans isomers and usually has been used in the preparation of several ruthenium–bipyridine species. Despite the possibility to have contamination of a specie in another, there is no analytical control involving the characterization of both complexes. Based on this we have proposed the use of high-performance liquid chromatography (HPLC) as an analytical technique to control the purity of cis and trans isomers. The separation was performed using a CLC-ODS column. The cis isomer eluted at 9.4 min while trans isomer eluted at 4.3 min. In aqueous solution the trans and cis isomer configurations were confirmed by NMR spectra (¹H). The attribution of cis isomer was also made based on the X-ray crystal structure (monoclinic, P2_1/c, a=12.320(2), b=13.852(2), c=34.220(3) Å, β=91.89(1)°, Z=8) which is reported. The six-coordinated ruthenium atom is chelated by two bipyridines and two molecules of H₂O.     

Synthesis,structure, and electrochemical behavior of a new dinuclear Rh(III) complex bridged by a bpp− ligand (bpp− = 3,5-bis(2-pyridyl)pyrazolate)

The new dinuclear rhodium complex [(Cp*RhCl)₂(bpp)](PF₆) ([1](PF₆), Cp* = pentamethylcyclopentadienyl, bpp = 3,5-bis(2-pyridyl)pyrazolate) was synthesized by the reaction of [Cp*RhCl₂]₂ with 3,5-bis(2-pyridyl)pyrazole (bppH). [1](PF₆) was characterized by ¹H- and ¹³C{¹H}-NMR spectroscopy and X-ray diffraction. The distance between the two Rh atoms in [1](PF₆) is 4.746(3) Å. A cyclic voltammogram of [1](PF₆) in acetonitrile shows three-step reduction peaks at E_pc = − 1.44, − 1.68 and − 1.88 V (vs. Fc⁺/Fc), which are assigned to the reduction of the two Rh(III) centers and the bpp⁻ ligand, respectively. [1](PF₆) catalyzes the reduction reaction of NAD⁺ (nicotinamide adenine dinucleotide) using HCO₂⁻ as a reductant.